The invention relates to data transmission systems and particularly to data transmission between a central office terminal for a telephone system and remote customer premises, each of which is connected to the telephone system by conventional telephone lines.
Initial concepts for interconnecting residents of a city concentrated on a "wired city" concept whereby integrated digital services would be provided to each subscriber's premises over fiber optic or coaxial cable networks. In recent years however, emphasis has shifted to integrated voice and data transmission systems capable of operating over telephone subscriber loops which are in place today.
Data voice modems are in existence which permit the telephone line to be selectively used for analog voice transmissions over the telephone handset or for the transmission of data. Similarly other data transmission schemes such as FSK, PSK, and AM modulation techniques have been developed. These technologies have inherent limitations such as cross talk, data quality, error rate, signal strengths and security.
Spread spectrum technology, which was originally developed for military uses, has been applied in a few recent developments to overcome the inherent limitations of previous technologies. U.S. Pat. Nos. 4,425,642, 4,426,661 and 4,475,208, show prior applications of spread spectrum to data transmissions. It is not believed, however, that any of the prior developments has been sufficiently integrated into a telephone subscriber network such that all subscribers on all exchanges can be connected to not only the telephone utility but any other utility or service organization including those which transmit various forms of data and information to subscribers.